After slashing her younger brother's neck, Roksana Sikorski moved on to stab her 11-year-old sister, according to police, but was spooked when both of them started screaming, prosecutors said

A suburban Detroit girl will spend 10 to 20 years in prison for hatching a plot to kill her family at the age of 15 with the help of her older boyfriend.

Roksana Sikorski, now 17, apologized to her parents in Wayne County Circuit Court before being handed her sentence Monday. She was tried as an adult on charges that included assault with intent to murder and conspiracy to commit murder.

Sikorski was convicted of scheming with her then-boyfriend Michael Rivera, eight years her senior, to murder her family members by stabbing them to death.

It was the night of Oct. 17, 2014, when the 15-year-old surveyed her parent’s kitchen inside the family’s upscale Plymouth Township home before carefully selecting a 6-8-inch filet knife and heading to her little brother's bedroom, according to police.

"I feel like dad is waking. He's moving but snoring. Babe..?" Sikorski wrote in one message to Rivera, according to WDIV-TV, to which he responded, "Baby im here just cut the throat quickly on both of them."

Sikorski at one point showed doubts, the texts showed, writing, "Babe I can't f----ing do it. I'm too scared. I want u to do it.... :( Plzz baby plzz. He kept waking up."

After stabbing her younger brother, the high school student moved on to her 11-year-old sister, according to police, but was spooked when both of the children started screaming. She then ran out of the house before she was able to carry out the planned attack on the rest of her family, police said.

"She still can't believe that she did it," her lawyer, Leslie Posner, told NBC News. "She's vivacious and outgoing. She gets A's in every class. She's tutoring other students. It was just a bad event."

Posner claimed the "sweet, little, diminutive 15-year-old" was "petrified" of Rivera. The two had met on Facebook the previous spring.

Roksana Sikorski and her two siblings were adopted by Laurene and Jeff Sikorski from an abusive family in Poland. Prior to the attack, her parents had filed a statutory rape complaint against her older boyfriend after learning of their relationship. The defense argued that is when Rivera convinced her into the murders. After further investigation, the rape charge was dismissed.

"Nothing will benefit this child by sending her to jail,” Laurene Sikorski said Monday in their final plea before the judge, WDIV-TV reports. “She made some poor choices that led her to this conviction … How will sentencing her as an adult help her? Is this justice?"

Judge James Callahan told the family he would try to request Sikorski be housed in a juvenile facility until she turns 18.

“I would like to apologize to my family for not being the daughter they wished I could be,” Sikorski said at her sentencing. “I promise I will get better, no matter what happens.”